Radiation emitting or receiving optoelectronic semiconductor chip

ABSTRACT

An optoelectronic semiconductor chip includes a multiplicity of active regions, arranged at a distance from one another, and a reflective layer arranged at an underside of the multiplicity of active regions, wherein at least one of the active regions has a main extension direction, one of the active regions has a core region formed with a first semiconductor material, the active region has an active layer, covering the core region at least in directions transversely with respect to the main extension direction of the active region, the active region has a cover layer formed with a second semiconductor material and covers the active layer at least in directions transversely with respect to the main extension direction of the active region, and the reflective layer reflects electromagnetic radiation generated during operation in the active layer.

TECHNICAL FIELD

This disclosure relates to an optoelectronic semiconductor chip isspecified.

BACKGROUND

There is a need to provide an optoelectronic semiconductor chip whichcan be operated particularly efficiently.

SUMMARY

We provide an optoelectronic semiconductor chip including a multiplicityof active regions arranged at a distance from one another, and areflective layer arranged at an underside of the multiplicity of activeregions, wherein at least one of the active regions has a main extensiondirection, one of the active regions has a core region formed with afirst semiconductor material, the active region has an active layercovering the core region at least in directions transversely withrespect to the main extension direction of the active region, the activeregion has a cover layer formed with a second semiconductor material andcovers the active layer at least in directions transversely with respectto the main extension direction of the active region, and the reflectivelayer reflects electromagnetic radiation generated during operation inthe active layer.

We also provide an optoelectronic semiconductor chip including amultiplicity of active regions arranged at a distance from one another,and a reflective layer arranged at an underside of the multiplicity ofactive regions, wherein at least one of the active regions has a mainextension direction, one of the active regions has a core region formedwith a first semiconductor material, the active region has an activelayer covering the core region at least in directions transversely withrespect to the main extension direction of the active region, the activeregion has a cover layer formed with a second semiconductor material andcovers the active layer at least in directions transversely with respectto the main extension direction of the active region, the reflectivelayer reflects electromagnetic radiation generated during operation inthe active layer, at least a large portion of the active regions have acurrent spreading layer, covering the cover layer at least in directionstransversely with respect to the main extension direction, and thecurrent spreading layer is transmissive to electromagnetic radiationgenerated during operation in the active layer, and an insulationmaterial is arranged between the multiplicity of active regions, and theinsulation material is transmissive to electromagnetic radiationgenerated during operation in the active layer and the insulationmaterial surrounds the active regions at least in directionstransversely with respect to the main extension direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example of an optoelectronic semiconductor chip in aschematic perspective illustration.

FIGS. 2A to 2M show schematic sectional illustrations of a method ofproducing an optoelectronic semiconductor chip.

FIGS. 3A to 3L show schematic sectional illustrations of a furthermethod of producing an optoelectronic semiconductor chip.

DETAILED DESCRIPTION

Our optoelectronic semiconductor chip is, in particular, aradiation-emitting optoelectronic semiconductor chip. By way of example,it is an optoelectronic semiconductor chip which emits UV radiation,visible light or infrared radiation during operation. The optoelectronicsemiconductor chip is, in particular, a light-emitting diode chip.Furthermore, it is possible for the semiconductor chip to be aradiation-receiving optoelectronic semiconductor chip, for example, asolar cell or a photodiode.

The optoelectronic semiconductor chip may comprise a multiplicity ofactive regions arranged at a distance from one another. During operationof the optoelectronic semiconductor chip, electromagnetic radiation isgenerated in the active regions and at least partly leaves thesemiconductor chip.

The optoelectronic semiconductor chip comprises a multiplicity of activeregions each arranged at a distance from one another. In this case, itis possible for the active regions at an underside and/or at a top sideto connect to one another by a further element. In this case, the activeregions are spaced apart from one another in a region between theirunderside and their top side and are not connected to one another there.

The active regions can be arranged, for example, in the manner of aregular lattice. That is to say that the active regions are arranged atpredefined distances from one another. By way of example, in a plan viewof the top sides of the active regions, a regular lattice structure isdiscernible such as the structure of a rectangular lattice or of atriangular lattice, for example. However, a random distribution of theactive regions is also possible.

The optoelectronic semiconductor chip may comprise a reflective layerarranged at the underside of the multiplicity of active regions. In thiscase, it is possible for the optoelectronic semiconductor chip tocomprise a single reflective layer, which connects all active regions ofthe optoelectronic semiconductor chip to one another at their underside.In this case, the active regions can directly adjoin the reflectivelayer at least in places at their undersides.

The reflective layer can be electrically conductive, in particular. Thereflective layer then serves for the electrical connection of the activeregions at whose underside it is arranged. By way of example, thereflective layer is formed with a metal for this purpose. For example,the reflective layer can contain one of the following metals or consistof one of the following metals: silver, aluminum, chromium, rhodium,nickel, platinum, tungsten, titanium.

Furthermore, it is possible for the reflective layer to be electricallyinsulating at least in places. The reflective layer can then comprise adielectric mirror or consist of such a dielectric mirror.

At least one of the active regions may have a main extension direction.That is to say that the active region does not extend to the same extentin every spatial direction. Rather, there is a preferred direction, themain extension direction, in which the active region has its greatestextension.

By way of example, the active region can have the form of a cylinder,the form of a truncated cone or the form of a prism, in particularhaving a hexagonal or triangular base surface. The main extensiondirection is then that direction in which the height of the cylinder orof the truncated cone is determined. In other words, the at least oneactive region is formed by an elongated three-dimensional body and, forexample, does not have the form of a sphere or of a cube. Furthermore,the active region is not a continuous unstructured area.

The at least one active region may have a core region formed with afirst semiconductor material. In this case, the first semiconductormaterial has a first conduction type. By way of example, the firstsemiconductor material is n-conducting. The first semiconductor materialcan be based, for example, on an n-doped III-V semiconductor materialsystem. By way of example, the first semiconductor material is based onan n-doped nitride semiconductor material system. In particular, thefirst semiconductor material can then be based on n-conducting GaN,InGaN, AlGaN or AlInGaN.

The core region of the active region extends in particular along themain extension direction and can have the same form as the activeregion. If the active region is in the form of a cylinder or prism, forexample, then the core region can also have the form of a cylinder. Thecore region can then be, in particular, a solid body consisting of thefirst semiconductor material.

The at least one active region may comprise an active layer, whichcovers the core region at least in directions transversely with respectto the main extension direction of the active region. The core regionhas a lateral surface, for example, which can be covered in particularcompletely with the material of the active layer. In this case, the coreregion can directly adjoin the active layer. During operation of theoptoelectronic semiconductor chip, the radiation generated by theoptoelectronic semiconductor chip is generated in the active region, inparticular, in the active layer. The active layer preferably has auniform thickness within the scope of the production tolerance.

The at least one active region may have a cover layer formed with asecond semiconductor material and covers the active layer at least indirections transversely with respect to the main extension direction ofthe active region. By way of example, the active layer is then arrangedbetween the cover layer and the core region. In this case, the coverlayer can completely cover the active layer, in particular. The coverlayer preferably has a uniform thickness within the scope of theproduction tolerance.

The second semiconductor material is a semiconductor material of asecond conduction type, which differs from the first conduction type. Inparticular, the second semiconductor material can be based on the samesemiconductor material system as the first semiconductor material, butcan in this case have a different doping. If the first semiconductormaterial is formed in an n-conducting fashion, for example, then thesecond semiconductor material is formed in a p-conducting fashion. Forexample, the second semiconductor material is based on p-GaN, p-InGaN,p-AlGaN or p-AlInGaN, if the first semiconductor material is based onn-GaN, n-InGaN, n-AlGaN or n-AlInGaN.

The reflective layer may be designed to reflect electromagneticradiation generated during operation in the active layer. That is to saythat the reflective layer is formed with a material which is reflectivefor the electromagnetic radiation generated in the active layer, and thereflective layer is arranged such that at least some of theelectromagnetic radiation generated by the active layer impinges on thereflective layer. The electromagnetic radiation leaves theoptoelectronic semiconductor chip, for example, at a side lying at aside of the active region facing away from the reflective layer.

The semiconductor chip may comprise a multiplicity of active regionsarranged at a distance from one another. Furthermore, the optoelectronicsemiconductor chip comprises a reflective layer arranged at an undersideof the multiplicity of active regions. In this case, at least one of theactive regions has a main extension direction, the active region has acore region formed with a first semiconductor material, the activeregion has an active layer covering the core region at least indirections transversely with respect to the main extension direction ofthe active region, the active region has a cover layer formed with asecond semiconductor material and covers the active layer at least in adirection being transverse to the main extension direction of the activeregion, and the reflective layer reflects electromagnetic radiationgenerated during operation in the active layer.

In this case, the optoelectronic semiconductor chip preferably comprisesa multiplicity of active regions constructed in an identical type offashion, for example. These active regions can then be identicallywithin the scope of the production tolerance. That is to say that eachof the active regions then comprises a core region, an active layer anda cover layer, which have a respectively identical material compositionwithin the scope of the production tolerance. In particular, it ispossible for all active regions of the optoelectronic semiconductor chipto be identically within the scope of the production tolerance. However,it is also possible for the optoelectronic semiconductor chip tocomprise a multiplicity of active regions that are different at least inpart. For example, the active regions can differ from one another withregard to thickness and composition. Thus, different active regions canemit light of different colors such that the semiconductor chip emits,for example, white light overall.

Preferably, all active regions of the semiconductor chip are based on aIII-V semiconductor material system, in particular, on a nitridecompound semiconductor material.

“Based on nitride compound semiconductor material” means that the activeregions comprise or consist of a nitride compound semiconductormaterial, preferably Al_(n)Ga_(m)In_(1-n-m)N, where 0≦n≦1, 0≦m≦1 andn+m≦1. In this case, this material need not necessarily have amathematically exact composition according to the above formula. Rather,it can comprise, for example, one or a plurality of dopants andadditional constituents. For the sake of simplicity, however, the aboveformula includes only the essential constituents of the crystal lattice(Al, Ga, In, N), even if these can be replaced and/or supplemented inpart by small amounts of further substances.

The efficiency of, in particular, GaN-based light-emitting diodes islimited under operating current conditions by the so-called “droop”effect. This effect denotes a significant drop in efficiency as thecurrent or charge carrier density rises. Typical operating currents aretherefore distinctly beyond the maximum of the efficiency curve. Toadvance to higher efficiencies with the current remaining constant, areduction of the local charge carrier density is therefore advantageous.This could be achieved, for example, by enlarging the cross-sectionalarea of the optoelectronic semiconductor chip or by increasing thenumber of active layers. Both approaches have problems, however.

In this regard, enlarging the cross-sectional area is impracticable formany applications, for example, the use of the optoelectronicsemiconductor chip in a projection apparatus, since this enlargement isaccompanied by an increase in the etendue. Moreover, this solution isalso always associated with an increase in costs disproportional to theincrease in the cross-sectional area of the semiconductor chip.

Increasing the number and/the thickness of the active layer is limitedby the fact that barriers between the layers, brought about inparticular by piezo-fields, impede the charge carrier transport and thuscounteract a uniform energization of all the layers.

In the case of the optoelectronic semiconductor chip described here, theactive regions are, for example, “core-shell nano- or microrods”. As aresult of the radiation-emitting region of the optoelectronicsemiconductor chip being divided into a multiplicity of active regions,that is to say, for example, a multiplicity of core-shell nanorods, thesurface area through which electromagnetic radiation generated duringoperation in the semiconductor chip emerges from the active layers isincreased relative to an optoelectronic semiconductor chip comprising asingle active region that is unstructured, for example. The efficiencyof the semiconductor chip is increased in this way.

The reflective layer at an underside of the active regions alsocontributes directly to increasing the efficiency since theelectromagnetic radiation generated during operation can be directed ina preferred direction by the reflective layer.

On account of the fact that an optoelectronic semiconductor chipcomprises a multiplicity of active regions, a significant enlargement ofthe active area and thus an increase in efficiency under operatingcurrent conditions in conjunction with a reduced charge carrier densityare achieved. Furthermore, in the course of the epitaxial growth of theactive regions, which are at a distance from one another, by comparisonwith a closed two-dimensional layer, it is possible to achieve areduction of strains in the semiconductor material of the activeregions.

In particular, it is possible for an optoelectronic semiconductor chipto comprise more than 1000, preferably more than 10 000, in particularmore than 100 000 or more than 1 million, active regions.

The first semiconductor material may be deposited epitaxially onto agrowth substrate, wherein the optoelectronic semiconductor chip itselfno longer has a growth substrate and is therefore free of a growthsubstrate. In other words, the growth substrate is removed from theepitaxially deposited layers of the optoelectronic semiconductor chipafter completion of the active regions. This is a feature whichcharacterizes the optoelectronic semiconductor chip as subject mattersince, by analyzing the optoelectronic semiconductor chip, it ispossible to demonstrate that the growth substrate was removed from theepitaxially deposited layers.

The growth direction of the first semiconductor material may runsubstantially parallel to the main extension direction. That is to saythat, within the scope of the production tolerance, the growth directionof the first semiconductor material runs parallel to the main extensiondirection. The growth direction of the active region can run on theupper end of the core region optionally longitudinally with respect tothe main extension direction. The first semiconductor material of thecore region of the at least one active region is therefore grown in themain extension direction. The active layer and the cover layer of theactive region cover the core region in directions that run transverselywith respect to the growth direction of the semiconductor material ofthe core region.

The active region may have a length determined in the main extensiondirection. That is to say that the length of the active region ismeasured along the main extension direction. Furthermore, the activeregion has a diameter determined in a direction perpendicular to themain extension direction, that is to say running in a plane to which themain extension direction is perpendicular. The diameter can vary alongthe main extension direction. The ratio of length to maximum diameter ofthe active region, preferably of all the active regions of theoptoelectronic semiconductor chip, is in this case at least three, inparticular at least five, for example, between at least five and at most20.

In this case, the diameter of the active region can be between at least100 nm and at most 25 μm. With regard to improving the material quality,in particular with regard to reducing dislocations in the semiconductormaterial of the active region, active regions having a diameter of atleast 100 nm and at most 3 μm, in particular at most 1 μm, prove to beparticularly advantageous. In the case of such thin active regions,dislocations generally do not pervade the active region along its entirelength, but rather—on account of the small thickness—end afterrelatively short path lengths at a lateral surface of the active region,without extending over the entire active region. Furthermore, it ispossible for the dislocations to extend along the entire length of thecore region of the active region, but not to penetrate through theactive layer on the outer surface of the core region.

In this case, the active regions are preferably arranged with highdensity that is to say with a high filling factor. In this case, thefilling factor corresponds to the ratio of the area of the reflectivelayer adjoining the active regions to the total area of the top side ofthe reflective layer assigned to the active regions. The filling factoris preferably at least 20%, in particular at least 50%, for example atleast 75%. A particularly significant enlargement of the active area ofthe optoelectronic semiconductor chip is achieved as a result.

The active region may have a current spreading layer covering the coverlayer at least in directions transversely with respect to the mainextension direction, wherein the current spreading layer is transmissivefor electromagnetic radiation generated during operation in the activelayer. The current spreading layer serves to distribute an electriccurrent particularly uniformly over the cover layer. In this case, thecurrent spreading layer is in particular in direct contact with thecover layer and can cover the latter completely. If the cover layer isformed with a p-conducting nitride compound semiconductor material, forexample, then it has a relatively low transverse conductivity. Thecurrent spreading layer therefore leads to a more uniform energizationof the active layer of the active region. The current spreading layercovers the cover layer preferably as a layer having a uniform thicknesswithin the scope of the production tolerance.

The current spreading layer is transmissive to electromagnetic radiationgenerated in the active region. That is to say that the currentspreading layer is radiation-transmissive.

“Radiation-transmissive” means that the radiation-transmissive componentallows at least 75% of the electromagnetic radiation of the active layerthat enters it to pass through without absorbing said radiation. In thiscase, the radiation-transmissive component can be milky, cloudy orpellucid, transparent.

The current spreading layer may be formed with a transparent conductiveoxide (TCO). By way of example, materials such as ITO or ZnO aresuitable to form the current spreading layer.

The current spreading layer may extend over at least a large portion ofthe length of the active region. In particular, it is possible for thecurrent spreading layer to uniformly cover and in this case completelycover the cover layer over the entire length of the active region.

An insulation material may be arranged between the multiplicity ofactive regions, wherein the insulation material is transmissive toelectromagnetic radiation generated during operation in the activelayer, and the insulation material surrounds the multiplicity of activeregions at least in directions transversely with respect to the mainextension direction. In other words, the insulation material is filledinto the interspaces between the active regions and the insulationmaterial can fill, in particular completely fill, the interspaces. Inthis case, the insulation material is electrically insulating andradiation-transmissive. By way of example, materials such as aluminumoxide (AlO_(x)), silicon dioxide, silicon nitride or polymers aresuitable as insulation materials.

Besides an electrical decoupling of the individual active regions, theinsulation material provides for protection of the active regionsagainst mechanical damage, atmospheric gases and moisture. Furthermore,the insulation material can be used as a planarization layer to whichthe reflective layer is applied at least in places. For example, theinsulation material for this purpose terminates flush with the activeregions at the underside thereof. In this way, the reflective layer canbe applied to a smooth area formed by the undersides of the activeregions and the insulation material.

The insulation material may directly adjoin the outer surface of theactive region at least in places. For example, the insulation materialcompletely covers the lateral surface of each active region and theredirectly adjoins the outermost layer of the active region, in particularthe current spreading layer. In this case, the insulation materialembeds into the active regions.

A mask layer may be arranged at that side of the multiplicity of activeregions facing away from the reflective layer, wherein the mask layerhas for each of the active regions an opening penetrated by the firstsemiconductor material. To produce the active regions, for example, amask layer is applied to a layer composed of first semiconductormaterial. The mask layer has openings to the layer composed of firstsemiconductor material. The first semiconductor material forming thecore region of each active region then grows onto the layer composed offirst semiconductor material only in the region of the openings. Theform and the diameter of the openings in the mask layer determine theform of the cross section and the diameter of the core region of eachactive region. The mask layer remains in the completed optoelectronicsemiconductor chip. Its openings are penetrated by first semiconductormaterial.

The mask layer may be transmissive to electromagnetic radiationgenerated during operation in the active layer. For this purpose, themask layer can be formed, for example, from the same material as theinsulation layer.

A coupling-out layer formed with the first semiconductor material may bearranged at that side of the multiplicity of active regions facing awayfrom the reflective layer. The coupling-out layer is, for example, thatlayer composed of first semiconductor material to which the mask layeris applied and onto which—in the openings of the mask layer—the coreregions of the active regions are grown epitaxially. During operation ofthe optoelectronic semiconductor chip, a large portion, that is to sayat least 50%, in particular at least 75%, of the electromagneticradiation emitted by the optoelectronic semiconductor chip is coupledout from the semiconductor chip through the coupling-out layer. In thiscase, the coupling-out layer can have a regular or an irregularstructuring at its side facing away from the reflective layer, whichstructuring increases the probability of the coupling-out.

The first semiconductor material of the coupling-out layer may connectto the first material in the core region of the active regions throughthe openings in the mask layer. That is to say that the core regions ofthe active regions are monolithically integrated with the coupling-outlayer.

The active region may have a passivation layer at its underside facingthe reflective layer, the passivation layer directly adjoining thereflective layer and the core region of the active region. In otherwords, the cover layer and the active layer, if appropriate also thecurrent spreading layer, can be removed at the underside of the activeregion. As a result, it is possible, for example, for the active regionsto be contact-connected on the n-side by the reflective layer. Acontact-connection of the p-side of the active regions can then beeffected by a contact-connection of the current spreading layer, forexample. In this way, it is possible for that side of the coupling-outlayer facing away from the reflective layer to be free of a contactmaterial for the connection of the semiconductor chip.

Our optoelectronic semiconductor chip and methods of producing it asdescribed here are explained in greater detail below in conjunction withexamples and the associated figures.

In the figures, identical or identically acting constituent parts may ineach case be provided with the same reference signs. The illustratedconstituent parts and their size relationships among one another shouldnot be regarded as true to scale, in principle. Rather, individualconstituent parts such as, for example, layers, structures, componentsand regions may be illustrated with exaggerated thickness or sizedimensions to enable better illustration and/or to afford a betterunderstanding.

FIG. 1 shows a schematic perspective illustration of a first example ofan optoelectronic semiconductor chip. The optoelectronic semiconductorchip comprises a multiplicity of active regions 1. The active regions 1each have the form of a cylinder. Each active region 1 extends along themain extension direction R. The active regions 1 are arranged at thelattice points of a regular lattice, a triangular lattice in the presentcase. A unit cell 100 of the lattice is indicated in FIG. 1.

Each of the active regions comprises a core region 10. The core region10 is formed with an n-doped GaN-based first semiconductor material. Thecore region 10 likewise is in the form of a cylinder. The lateralsurface of the cylinder is completely covered by the active layer 11, inwhich electromagnetic radiation is generated during operation of theoptoelectronic semiconductor chip.

The active layer 11 is in the form of a hollow cylinder, the innersurface of which is completely covered with the first semiconductormaterial of the core region 10. The outer surface of the active layer 11is completely covered by a cover layer 12 formed with a p-dopedGaN-based second semiconductor material in the example in FIG. 1.

The outer surface of the cover layer 12 facing away from the activelayer 11 is completely covered with the current spreading layer 13. Thecurrent spreading layer 13 is radiation-transmissive to electromagneticradiation generated in the active layer 11 and consists of a TCOmaterial, for example, ITO.

Interspaces between the active regions 1 are filled with an insulationmaterial 4, which directly adjoins the outer surface of the currentspreading layer 13 facing away from the core region 10. The insulationmaterial 13 is transmissive to electromagnetic radiation generated inthe active layer 11 and is electrically insulated. By way of example,the insulation material 4 consists of silicon dioxide. The insulationmaterial 4 can be applied, for example, by spin-coating, vapordeposition, sputtering, ALD or CVD.

Each active region 1 has a passivation layer 14 at is underside 1 a,which passivation layer encloses the core region 10 in a ring-shapedmanner and directly adjoins the first semiconductor material of the coreregion 10. In the region of the passivation layer 14, the core region10, the active layer 11 and the cover layer 12 are removed orneutralized, for example, by ion implantation. In this case, the p-sidecan be contact-connected by the largely spreading metal contact of thereflective layer 2. Alternatively, in the region of the passivationlayer 14, the active layer 11, the cover layer 12 and the currentspreading layer 13 can be removed or neutralized, for example, by ionimplantation. In this case, the n-side connects via the reflectivelayer.

The passivation layer 14 can be formed with an electrically insulatingmaterial and consists of the insulation material 4, for example.Furthermore, it is possible for the passivation layer 14 to be producedby neutralization of semiconductor material.

A reflective layer 2 is arranged at the underside 1 a of the activeregions 1. The reflective layer 2 is provided to reflect electromagneticradiation generated in the active layer 11. In this case, the reflectivelayer 2 is preferably electrically conductive and serves for theelectrical connection of the active regions 1. On account of thepresence of the passivation layer 14, the reflective layer 2 connectsthe p-conducting cover layer 12 and the current spreading layer 13. Byway of example, the reflective layer 2 consists of silver.

A mask layer 5 is arranged at that side of the active regions 1 facingaway from the reflective layer 2. The mask layer 5 is formed with amaterial transmissive to the electromagnetic radiation generated in theactive layer 11 during operation. Furthermore, the mask layer 5 ispreferably electrically insulating. For this purpose, the mask layer 5can consist of silicon dioxide or silicon nitride, for example. The masklayer 5 has openings 5 a, the number of which corresponds to the numberof active regions 1 to the greatest possible extent. Through theopenings 5 a, the core region 10 of each active region 1 connects to acoupling-out layer 3.

The coupling-out layer 3 is formed with the same semiconductor materialas the core regions 10 of the active regions 1. The core regions 10 ofthe active regions 1 are grown epitaxially on the mask layer 5. In theopenings 5 a, the core regions 10, as a result of the epitaxial growth,are mechanically fixedly connected to the likewise epitaxially grownsemiconductor material of the coupling-out layer 3. The growth directionz of the epitaxial growth of the coupling-out layer 3 and of the coreregions 10 is parallel to the main extension direction R of the activeregions 1. The active regions 1 are arranged at a distance from oneanother in the plane x, y perpendicular to the main extension directionR.

At its side facing away from the mask layer 5, the coupling-out layer 3has coupling-out structures 30 formed by a random structuring of thesemiconductor material of the coupling-out layer 3. By way of example,this random structuring is produced by etching by KOH.

The diameter of the active regions 1 in the plane x, y is, for example,150 nm. The length of the active regions 1 is, for example, 1.5 μm inthe main extension direction R. During operation of the optoelectronicsemiconductor chip, electromagnetic radiation having a wavelength of 440nm is generated, for example, in the active layer 11.

With reference to the schematic sectional illustrations in FIGS. 2A to2M, a method of producing an optoelectronic semiconductor chip isexplained in greater detail.

FIG. 2A schematically shows a growth substrate 6 onto which thecoupling-out layer 3 formed with a first semiconductor material isdeposited epitaxially. The radiation-transmissive mask layer 5 with theopenings 5 a is applied to that surface of the coupling-out layer 3facing away from the growth substrate 6.

In conjunction with FIG. 2B the illustration shows that afterward thecore regions 10, which are likewise formed with the first semiconductormaterial, are deposited epitaxially onto the mask layer 5 and grow ontothe material of the coupling-out layer 3 only in the region of theopenings 5 a. Cylindrical or prism-shaped core regions 10 arise, forexample.

The active layer 11 is in each case deposited epitaxially onto the outersurface of the core regions 10. The active layer 11 later constitutesthe active shell of the active region 1 as shown in FIG. 2C.

In the next method step, FIG. 2D, the cover layer 12 is depositedepitaxially onto the active layer 11 of each active region 1. The coverlayer 12 completely covers the active layer 11.

In the subsequent method step, FIG. 2E, the current spreading layer 13is deposited onto the cover layer 12, for example, by sputtering orvapor deposition.

In the method step illustrated in FIG. 2F, the insulation material 4 isformed over the active regions 1 produced in this way. In this case, theinsulation material 4 fills interspaces between the active regions 1spaced apart from one another and also covers the active regions 1 attheir surface facing away from the growth substrate 6.

In the next method step, FIG. 2G, the active regions 1 are exposed byremoval of the insulation material 4. In this case, the active layer 11,the cover layer 12 and the current spreading layer 13 are also removedat that side of the active regions 1 facing away from the growthsubstrate 6, with the result that the core regions 10 of the activeregions 1 are exposed. In this case, the material removal can beeffected by means of etching and/or chemical mechanical polishing, forexample.

The electrically insulating passivation layer 14 is produced in aring-shaped region of each active region FIG. 2H.

Afterward, in FIG. 2I, the reflective layer 2 is applied to that side ofthe active regions 1 and of the insulation material 4 facing away fromthe growth substrate 6. Afterward, in FIG. 2J, a carrier 7 is applied tothat side of the reflective layer 2 facing away from the growthsubstrate 6.

FIG. 2K shows that the growth substrate 6 is subsequently removed. Whenthe growth substrate 6 consists of sapphire, this can be effected by alaser lift-off method. When the growth substrate 6 is formed withsilicon, chemical etching can also be effected to strip away the growthsubstrate 6.

This results in a structure, FIG. 2L, which is free of a growthsubstrate 6.

Finally, in FIG. 2M, the coupling-out structures 30 can be produced byetching, for example. The optoelectronic semiconductor chip produced inthis way can be provided with connections 8.

With reference to the schematic sectional illustrations in FIGS. 3A to3L, a further method of producing an optoelectronic semiconductor chipis explained in greater detail.

FIG. 3A schematically shows a growth substrate 6 onto which thecoupling-out layer 3 formed with an n-doped first semiconductor materialis deposited epitaxially. The radiation-transmissive mask layer 5 withthe openings 5 a is applied to that surface of the coupling-out layer 3facing away from the growth substrate 6.

FIG. 3B shows that, afterward, the core regions 10, which are likewiseformed with the first semiconductor material, are deposited epitaxiallyonto the mask layer 5 and grow onto the material of the coupling-outlayer 3 only in the region of the openings 5 a. Cylindrical orprism-shaped core regions 10 arise, for example.

The active layer 11 is in each case deposited epitaxially onto the outersurface of the core regions 10. The active layer 11 later constitutesthe active shell of the active region 1, as shown in FIG. 3C.

In the next method step, FIG. 3D, the cover layer 12 is depositedepitaxially onto the active layer 11 of each active region 1. The coverlayer 12 completely covers the active layer 11.

In the subsequent method step, FIG. 3E, the current spreading layer 13is deposited onto the cover layer 12, for example, by sputtering.

In the method step illustrated in FIG. 3F, the insulation material 4 isformed over and/or around the active regions 1 which have been produced.In this case, the insulation material 4 fills interspaces between theactive regions 1 spaced apart from one another and also covers theactive regions 1 at their surface facing away from the growth substrate6.

In the subsequent method step, FIG. 3G, in contrast to the previousmethod, now the core region 10 of the active regions 1 is not exposed,rather the insulation material 4 is removed until the current spreadinglayer 13 is exposed.

In the method step in FIG. 3H, the reflective layer 2 is applied to thatside of the active regions 1 and of the insulation material 4 facingaway from the growth substrate 6. The reflective layer 2 is thuselectrically conductively connected to the current spreading layer 13and, in contrast to the example in FIG. 2, connects the p-side of theactive regions 1.

Afterward, in FIG. 3I, a carrier 7 is applied to that side of thereflective layer 2 facing away from the growth substrate 6.

FIG. 3J shows that the growth substrate 6 is subsequently removed. Whenthe growth substrate 6 consists of sapphire, this can be effected by alaser lift-off method. When the growth substrate 6 is formed withsilicon, chemical etching can also be effected to strip away the growthsubstrate 6.

This results in a structure, FIG. 3K, which is free of a growthsubstrate 6.

Finally, in FIG. 3L, the coupling-out structures 30 can be produced byetching, for example. The optoelectronic semiconductor chip produced inthis way can be provided with connections 8.

As an alternative to the epitaxial growth of the core regions 10 throughthe openings 5 a of the mask layer 5, the core region 10 can also beproduced by a structuring such as an etching, for example, of apreviously grown, closed layer. The masking layer 5 between coupling-outlayer 3 and active regions 1 is then not present, but can be replaced bya passivation layer applied subsequently. Optionally, the structure isannealed, for example, by wet-chemical KOH treatment to improve thematerial quality of the core regions thus produced. Subsequent,optional, overgrowth with first semiconductor material, with activelayer 11 and cover layer 12 is then effected as described above.

Our chips and methods are not restricted to the examples by thedescription examples, but rather encompass any novel feature and alsoany combination of features, which includes in particular anycombination of features in the appended claims, even if the features orcombinations themselves are not explicitly specified in the claims orexamples.

The invention claimed is:
 1. An optoelectronic semiconductor chipcomprising: a multiplicity of active regions arranged at a distance fromone another, and a reflective layer arranged at an underside of themultiplicity of active regions, wherein at least one of the activeregions has a main extension direction, one of the active regions has acore region formed with a first semiconductor material, the activeregion has an active layer covering the core region at least indirections transversely with respect to the main extension direction ofthe active region, the active region has a cover layer formed with asecond semiconductor material and covers the active layer at least indirections transversely with respect to the main extension direction ofthe active region, the reflective layer reflects electromagneticradiation generated during operation in the active layer, and aninsulation material is arranged between the multiplicity of activeregions, is transmissive to electromagnetic radiation generated duringoperation in the active layer, and surrounds the active regions at leastin directions transversely with respect to the main extension direction.2. The optoelectronic semiconductor chip according to claim 1, whereinthe active regions are based on a nitride compound semiconductormaterial, the first semiconductor material is deposited epitaxially ontoa growth substrate, and the optoelectronic semiconductor chip is free ofthe growth substrate, a growth direction of the first semiconductormaterial is substantially parallel to the main extension direction, atleast a large portion of the active regions have a length determined inthe main extension direction and have a diameter determined in a planeperpendicular to the main extension direction, and the ratio of lengthto diameter is at least three, at least a large portion of the activeregions have a current spreading layer covering the cover layer at leastin directions transversely with respect to the main extension direction,and the current spreading layer is transmissive to electromagneticradiation generated during operation in the active layer, the currentspreading layer is formed with a transparent conductive oxide, thecurrent spreading layer extends over at least a large portion of thelength of the active region, an insulation material is arranged betweenthe multiplicity of active regions, and the insulation material istransmissive to electromagnetic radiation generated during operation inthe active layer and the insulation material surrounds the activeregions at least in directions transversely with respect to the mainextension direction, the insulation material directly adjoins thecurrent spreading layer at least in places, the reflective layerdirectly adjoins the insulation material in places, and at least a largeportion of the active regions have a passivation layer at theirunderside facing the reflective layer, said passivation layer directlyadjoining the reflective layer and the core region of the active region.3. The optoelectronic semiconductor chip according to claim 1, whereinthe first semiconductor material is epitaxially deposited onto a growthsubstrate, and the optoelectronic semiconductor chip is free of thegrowth substrate.
 4. The optoelectronic semiconductor chip according toclaim 1, wherein a growth direction of the first semiconductor materialis substantially parallel to the main extension direction.
 5. Theoptoelectronic semiconductor chip according to claim 1, wherein theactive region has a length determined in the main extension direction,the active region has a diameter determined in a plane beingperpendicular to the main extension direction, and the ratio of lengthto diameter is at least three.
 6. The optoelectronic semiconductor chipaccording to claim 1, wherein the current spreading layer is formed witha transparent conductive oxide.
 7. The optoelectronic semiconductor chipaccording to claim 1, wherein the active region has a length determinedin the main extension direction and the current spreading layer extendsover at least a large portion of the length of the active region.
 8. Theoptoelectronic semiconductor chip according to claim 1, wherein theinsulation material directly adjoins an outer surface of the activeregion at least in places.
 9. The optoelectronic semiconductor chipaccording to claim 1, wherein the active region has a current spreadinglayer covering the cover layer at least in directions transversely withrespect to the main extension direction and the insulation materialdirectly adjoins the current spreading layer at least in places.
 10. Theoptoelectronic semiconductor chip according to claim 1, wherein thereflective layer directly adjoins the insulation material in places. 11.The optoelectronic semiconductor chip according to claim 1, wherein themask layer is transmissive to electromagnetic radiation generated duringoperation in the active layer.
 12. The optoelectronic semiconductor chipaccording to claim 1, wherein a coupling-out layer is arranged at a sideof the multiplicity of active regions facing away from the reflectivelayer, said coupling-out layer being formed with the first semiconductormaterial.
 13. The optoelectronic semiconductor chip according to claim1, wherein a coupling-out layer is arranged at a side of themultiplicity of active regions facing away from the reflective layer,said coupling-out layer being formed with the first semiconductormaterial, and the first semiconductor material of the coupling-out layerconnects to the first semiconductor material in the core regions of theactive regions through the openings in the mask layer.
 14. Theoptoelectronic semiconductor chip according to claim 1, wherein theactive region has a passivation layer at its underside facing thereflective layer, said passivation layer directly adjoining thereflective layer and the core region of the active region.
 15. Anoptoelectronic semiconductor chip comprising: a multiplicity of activeregions arranged at a distance from one another, and a reflective layerarranged at an underside of the multiplicity of active regions, whereinat least one of the active regions has a main extension direction, oneof the active regions has a core region formed with a firstsemiconductor material, the active region has an active layer coveringthe core region at least in directions transversely with respect to themain extension direction of the active region, the active region has acover layer formed with a second semiconductor material and covers theactive layer at least in directions transversely with respect to themain extension direction of the active region, the reflective layer isconfigured to reflect electromagnetic radiation generated duringoperation in the active layer, and the active region has a currentspreading layer covering the cover layer at least in directionstransversely with respect to the main extension direction, and thecurrent spreading layer is transmissive to electromagnetic radiationgenerated during operation in the active layer.
 16. An optoelectronicsemiconductor chip comprising: a multiplicity of active regions arrangedat a distance from one another, and a reflective layer arranged at anunderside of the multiplicity of active regions, wherein at least one ofthe active regions has a main extension direction, one of the activeregions has a core region formed with a first semiconductor material,the active region has an active layer covering the core region at leastin directions transversely with respect to the main extension directionof the active region, the active region has a cover layer formed with asecond semiconductor material and covers the active layer at least indirections transversely with respect to the main extension direction ofthe active region, the reflective layer is configured to reflectelectromagnetic radiation generated during operation in the activelayer, and a mask layer is arranged at a side of the multiplicity ofactive regions facing away from the reflective layer, and the mask layerhas, for each of the active regions, an opening through which the firstsemiconductor material penetrates.